a) Field of the Invention
This invention relates to a thermoelectric apparatus such as a thermoelectric cooling apparatus or a thermoionic electricity generator, and especially to a thermoelectric apparatus which does not undergo much performance degradation even through repeated heat cycles and has excellent operation reliability and long service life.
b) Description of the Related Art
In a conventional thermoelectric apparatus, a group of thermoelectric elements is arranged between thermal conductors, and is fixed in place by fastening the thermal conductors together with plural screws with a thermally-conductive grease applied between each thermal conductor and the group of thermoelectric elements to improve their thermal contact.
As the screws, those made of metal or plastics are used. Metal screws have sufficient strength for the fixing of the group of thermoelectric elements. These metal screws are used in combination of heat-insulating washers because their thermal conductivity is high when used by themselves. On the other hand, plastic screws have low thermal conductivity but due to low mechanical strength, require additional reinforcement by an adhesive or the like.
Fastening force of such screws is needed for assuring thermal conductance between the thermal conductors and the group of thermoelectric elements and also for fixing the group of thermoelectric elements in place. Incidentally, the group of thermoelectric elements is sealed at an outer periphery thereof by silicone rubber or the like for waterproofing.
Since the group of thermoelectric elements is fixed in place by fastening the thermal conductors together with the plural screws in the conventional thermoelectric apparatus as described above, it is difficult to apply uniform pressure to the group of thermoelectric elements. Some of the thermoelectric elements are therefore subjected to localized load, so that they may be broken.
Screws made of a material of relatively low thermal conductivity, for example, stainless steel screws or iron screws are used as the above-described metal screws. The screws of such a material has a smaller coefficient of thermal expansion than the thermal conductors and the thermoelectric elements. During use of the thermoelectric apparatus, the thermal conductors and thermoelectric elements move due to expansion and shrinkage. Such movements of the thermal conductors and thermoelectric elements are restrained by the screws, so that large compression or tensile stress is repeatedly applied to the thermoelectric elements, possibly resulting in breakage of the thermoelectric elements.
Plastic screws, on the other hand, are low in mechanical strength so that they lack long-term reliability. Moreover, they are accompanied by such a drawback that they are unable to provide strength sufficient to withstand a drop and impact test for a thermoelectric apparatus.